1. Field of the Invention:
The present invention relates to a process for determining the spacing between a heater and a showerhead, and more particularly to a process for determining the spacing between a heater and a showerhead at a temperature higher than 350xc2x0 C.
2. Description of the Prior Art:
In a chemical vapor deposition reaction chamber, the showerhead plays the role of distributing gas. After a period of deposition, undesired materials will attach on the showerhead surface. Consequently, during the subsequent deposition, the thin film deposition properties including the deposition rate, stress and etch rate are adversely affected. This makes it difficult to maintain the process performance stable. Therefore, it is necessary to clean the showerhead or even change a new showerhead.
The spacing between the heater and showerhead has influence on the deposition uniformity. Therefore, when the showerhead is cleaned or changed and installed back above the heater in the chemical vapor deposition reaction chamber, the spacing between the showerhead and the heater should be accurately determined and controlled to meet the standard spacing value.
Nowadays, the device or sensor for determining the spacing between the heater and showerhead can not withstand high temperatures above 350xc2x0 C., and deteriorates at such high temperatures. Therefore, the process for determining the spacing between the heater and showerhead is usually conducted at low temperatures. However, when the chemical vapor deposition (CVD) process proceeds, the heater is increased to a high temperature above 350xc2x0 C. Thus, the actual spacing at high temperatures during the CVD process is different from the spacing determined at low temperatures. That is, when the spacing determined at low temperatures meets the standard value, the actural spacing at high temperatures during the CVD process does not meet the standard value.
Therefore, a process for determining the spacing between the heater and showerhead at high temperatures by means of sandwiching a lump of aluminum foil between the heater and the showerhead has been developed recently. Taking Novellus SEQUEL chemical vapor deposition machine as an example, the process chamber is first evacuated; after the heater is increased to 400xc2x0 C., the chamber is opened and three previously kneaded lumps of aluminum foil are placed on the locations where the respective showerheads are to be placed on the heater. Then, the showerheads are lowered to a predetermined position. The chamber is evacuated, and heated to 400xc2x0 C. again. Then, the chamber is opened, the lumps of aluminum foil which have been pressed flat by the showerheads are taken out and determined their thickness with vernier calipers. The thickness is the spacing between the heater and showerhead. If the spacing determined does not meet the standard value, then adjust the spacing and repeat the above-mentioned determination steps until the spacing meets the standard value.
However, in the determination process, the lumps of aluminum foil should be taken out and determined with great care lest the accuracy is influenced. In addition, in order to make the spacing meet the standard value, many times of determination should be conducted, aluminum foil lumps should be taken out for determination for many times, the reaction chamber should be opened and closed for many times, and the chamber should be evacuated for many times. This makes the entire process very lengthy and the cost is inevitably increased.
Therefore, the object of the present invention is to solve the above-mentioned problems and to provide a process for determining the spacing between a heater and a showerhead. The determination process of the present invention can be conducted at high temperatures above 350xc2x0 C. In addition, the spacing value can be determined without opening the deposition reaction chamber, which is very convenient and with high accuracy, and the cost can be decreased.
To achieve the above objects, the process for determining the spacing between a heater and a showerhead according to the present invention includes the steps of:
(a) placing at least one variable capacitor between the heater and the showerhead, such that the spacing between the heater and the showerhead is in a predetermined relationship to the capacitance of the variable capacitor;
(b) measuring the capacitance of the variable capacitor; and
(c) converting the capacitance into the spacing between the heater and the showerhead.